LEDs, LED drivers guidelines needed

Forum 2005-2010 (read only) General Frequently-Asked Questions
1

Good day!

LEDs seems to come without any datasheets (they are simply LEDs :)), so I've collected some questions. Please point me to any faq\tutorials if there are some of them.

  • What LEDs needs drivers instead of simple resistor? High-power LEDs labeled 1W/3W or any other types?

  • What are simple and proven LED drivers (IC or discrete elements based)?

  • What are "bright LEDs"? They look like simple 5mm LEDs are they just more effective?

  • I can't get RGB LED locally, so my plan is to use 3 separate LEDs for things like 'mood lamps'. How to "calibrate" them to work together (red ones seems to be lighter, green -- darker etc).

  • I want to drive LEDs using 8-bit PWM. I assume that simple LEDs with 20mA current can be driven directly from pins. For more powerful LEDs what is the best: use separate transistors or things like ULN2803A (seems to be an array of Darlington transistors in one case)?

  • I want to drive 6 LEDs (two for each color) from 3 PWM pins via ULN2803A with appropriate resistors for each LED. Does this make sense?

Thanks in advance!

2

This set of question gets asked abour 5 times EACH DAY on this forum. Just read other posts with LED. (There is a search function to find those posts)

Balancing the RGB LEDs (whether seperate or in one) is a matter of driving the bright red LED at a lower current than it can handle, or rather you purposfully use a higher resistor than needed. If you do not have any hard facts (mA mcd) of the LED just use your eyes and try a few values. In the end, no matter what you have calculated, you still will decide if it "looks even". :wink:

Good luck.

3

Check out the LED tutorial from Adafruit.
http://www.ladyada.net/learn/arduino/LEDs.html

Brighter LEDs usually take more voltage or have a smaller smaller viewing angle . This means that while the LED is brighter, you have to look at it more straight on to see it.

4

Thank for the responses, here are links (for googlers like me):

http://www.ladyada.net/learn/arduino/LEDs.html
(awesome tutorial, thanks Pauly!)

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1269902243/15
http://www.thebox.myzen.co.uk/Tutorial/Power_Examples.html
(about darlington drivers)